1. Field of the Invention
The present invention relates to a printing system and to a printing control apparatus, such as a personal computer, and a printing apparatus that constructs this printing system.
2. Description of the Related Art
There are printing systems in which a host computer (referred to simply as a computer below) converts data created by an application or the like to bitmap data in a YMCK calorimetric system, etc., capable of being printed by a printing apparatus (referred to simply as a printer below), and then transmits the bitmap data to the printer. The computer in this printing system subjects input image data to a color conversion and quantization processing to convert the input image data to binary data or N-value data, which has a small number of gray levels in comparison with the original image, capable of being printed by the printer. In the course of this conversion processing, use is made of a conversion table to which reference is had in order to convert the calorimetric system of the original image created by the application or the like to the calorimetric system of the printer, and a conversion table to which reference is had in order to execute quantization processing.
By way of example, it is required that image data represented by luminance signals R (red), G (green) and B (blue) undergo a color conversion to image data represented by density signals Y (yellow), M (magenta) and C (cyan) used by the printer. There are many cases where YMC further include a K (black) component in accordance with the functions of the printer. In the color conversion, first the RGB data is subjected to a color correction (eight bits per each of R, G, B to eight bits per each of R, G, B). Next, the color conversion is performed (eight bits per each of R, G, B to eight bits per each of C, M, Y, K). Next, a tone correction is applied (eight bits per each of C, M, Y, K to eight bits per each of C, M, Y, K). Finally, quantization processing is executed (eight bits per each of C, M, Y, K to one bit per each of C, M, Y, K).
In these conversion or correction operations, use is made of conversion tables prepared in advance and stored in the computer. The conversion tables used differ depending upon the type of printing medium used in printing and upon the designated print quality. Consequently, the number of each of these conversion tables is equivalent to the number of combinations of types of printing media and print qualities.
On the other hand, there are also printing systems in which the computer transmits multi-valued image data to the printer and the data is converted by the printer to data suited to the printer. The image data that is sent from the personal computer to the printer in this printing system is image data in the bitmap format in the RGB calorimetric system (this data will be referred simply as “bitmap data”). Since bitmap data generally has a large data size, it is transmitted to the printer after being compressed in a format compliant with JPEG or the like. The above-described conversion processing is executed using a conversion table that is being held in the computer.
In general, an inexpensive printer will not have a large storage capacity in order to reduce cost. Often a printer with a small storage capacity cannot hold printing parameters such as conversion tables corresponding to all combinations of types of printing media and printing qualities. Furthermore, there are also cases where conversion tables held by a printer have been reduced in size and simplified, as by reducing the number of grid points. If use is made of a conversion table having few grid points, an input value corresponding to a grid point is converted to an output value stored in association with this grid point. However, when an input value that does not correspond to a grid point is converted, the output value that corresponds to this input value is calculated by an interpolation of the conversion table and this value is used in the conversion. This means that printed results having a higher image quality can be obtained by forming an image using a conversion table having many grid points rather than a simple conversion table held by a printer.
Accordingly, in order to obtain a high image quality with a printer having a small storage capacity, a technique in which printing parameters such as conversion tables suited to printing are transmitted from a computer to a printer together with print data has been proposed (e.g., Japanese Patent Laid-Open No. 11-175284). This cited patent document describes a printing control apparatus in which printing parameters conforming to the type of printing medium and print quality designated by a printing setting unit (referred to as a “printer driver user interface” below) are transmitted to a printer upon being attached to multi-valued data. In accordance with this technique, the conversion tables being held by the printer are only those that conform to the designated type of printing medium and print quality. As a result, high-quality printing can be expected even with a printer having a small storage capacity.
Furthermore, the printer is equipped with a mechanism (referred to as a “medium sensor” below) for sensing the type of printing medium. If the type of printing medium actually loaded in the printer is sensed and the printer driver is notified of the type, then it will be possible for the printer driver to select printing parameters that conform to the reported information concerning the type of printing medium and the print quality.
However, there are instances where the user replaces the printing medium with another after the printer has acquired the type of printing medium from the printer. In such case there will be a discrepancy between the type of printing medium used and the type of printing medium to which reference is had in order to select the printing parameters. As a consequence, printed results having a high quality cannot be obtained.